AC-DC Interface Grounding Switch for Fast Fault Disconnection
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Solution Overview
Problem
Existing interface arrangements between AC and DC systems face challenges in safely and quickly disconnecting the DC system from the AC system during faults, causing stress on electronic components due to overvoltage and fault current issues.
Innovation Solution
An interface arrangement with switching elements, circuit breakers, and a breaker assisting unit that includes switches in series with impedance elements, where the switches are closed to ensure zero-crossings of fault currents before opening the circuit breakers, thereby protecting the converter from stress and ensuring safe disconnection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If circuit breakers are used to disconnect the DC system from the AC system during faults, then safety is improved, but the disconnection cannot be performed immediately because the current has to be alternating with zero-crossings
Solution Approach 1:
The grounding switch is closed in advance before the fault occurs, establishing a pre-configured path to ground. When a fault occurs, the circuit breaker can immediately open without waiting for current zero-crossings, because the grounding switch already provides the alternative current path. This preliminary configuration resolves the contradiction by preparing the system ahead of time.
Solution Approach 2:
The grounding switch acts as an intermediary element between the DC system and ground. It mediates the fault current by providing an alternative path to ground, allowing the circuit breaker to open instantly without being constrained by current zero-crossings. This intermediary component enables both immediate disconnection and maintained safety.
2Speed
If circuit breakers are opened immediately during faults, then disconnection speed is improved, but the current cannot be interrupted properly because it requires alternating current with zero-crossings
Solution Approach 1:
The grounding switch is closed in advance, creating a pre-established alternative current path. This preliminary action allows the circuit breaker to open immediately at fault occurrence without waiting for current zero-crossings, while the grounding switch ensures the fault current is properly directed to ground through the alternative path.
Solution Approach 2:
The grounding switch serves as an intermediary that accepts the fault current when the circuit breaker opens. It mediates the current interruption by providing a controlled path to ground, enabling fast disconnection while maintaining reliable current interruption through the alternative grounding path.
3Speed
If grounding switch is closed during normal operation, then fault current path is prepared, but it causes unwanted current flow and stress on components during normal operation
Solution Approach 1:
The grounding switch transitions from a static to a dynamic state based on system conditions. It is closed in advance (before fault) to prepare the path, then opened after the circuit breaker interrupts the fault current. This dynamic operation ensures the grounding path is available when needed but not present during normal operation, avoiding unwanted current flow and component stress.
Solution Approach 2:
The grounding switch operates periodically - closed before fault occurrence to prepare the current path, then opened after fault interruption. This periodic switching ensures the grounding path is temporarily available for fast fault response but removed during normal operation to prevent harmful effects, thus resolving the contradiction between fast response and component protection.
Data Source
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AI summary
The present invention relates to an interface arrangement (20) for connection between an AC system (S1) and a DC system (S2) and to a method of disconnecting a DC system from an AC system. The arrangement includes a converter (22) for conversion between AC and DC having a DC side for connection to the DC system and an AC side for being coupled to the AC system, a set of circuit breakers (BR1, BR2, BR3) coupled between the AC side of the converter and the AC system and a breaker assisting unit (28) comprising a set of branches connected between the AC side of the converter and ground, where each branch includes a switch in series with an impedance element.